The Hijri year or era is the era used in the Islamic lunar calendar, beginning its count from 622 CE, the year of the migration of Muhammad and his followers from Mecca to Yathrib (later Medina), an event known as the Hijra. It is denoted in Arabic with a hāʾ (هـ), the first letter of Hijra. It is denoted in English by the abbreviation AH, which follows the format of the Dionysian era in representing a Latin phrase. Anno Hegirae (/ˈænoʊ ˈhɛdʒᵻriː/) means "in the year of the Hijra" and should technically precede dates in the manner of AD. More commonly, it is placed after the year.

Because the Islamic lunar calendar has only 354 days in its year, it slowly rotates within the Gregorian year. The year 2016 CE corresponds to the Islamic years AH 1437 – 1438.

Definition

The Hijri era is calculated according to the Islamic lunar calendar and not the Julian or Gregorian solar one. It thus does not begin on January 1 CE, but on the first day of the month of Muharram which occurred in 622 CE. Its Julian equivalent was April 19 but it is sometimes mistakenly placed on July 16. The error derives from the tabular Islamic calendar which was devised by later Islamic astronomers. This reckons time backwards according to the lunar calendar, which causes it to miss the three intercalary months (about 88 days) added to the then-lunisolar calendar between the time of the Hijra and AH 10, when Muhammad allegedly received a revelation prohibiting their use.